Field of the Invention
The present invention relates to a focus detection apparatus which performs focus detection of a phase difference method by obtaining pupil-divided images through an image pickup element including a plurality of pixels sharing one micro lens.
Description of the Related Art
Conventionally, a focus detection apparatus (an image pickup apparatus) including a plurality of divided photoelectric conversion devices (hereinafter, referred to as “PDs”) with respect to one pixel corresponding to one micro lens (hereinafter, referred to as an “ML”) which perform focus detection of phase difference method while taking an image has been known.
Japanese Patent Laid-open No. 2001-83407 discloses a configuration to obtain pupil-divided image signals by divided photoelectric conversion devices (hereinafter, referred to as “divided PDs”) to perform focus detection process of a phase difference method. In the configuration disclosed in Japanese Patent Laid-open No. 2001-83407, an imaging pixel signal is obtained by treating an added value output from the divided PDs corresponding to the same micro lens as an output of one pixel.
Japanese Patent No. 4691930 discloses a method of reading a part of the divided PDs (one of the divided PDs) in a non-destructive manner in order to improve characteristics of high sensitivity in a divided pixel structure, and then reading the added value of each of the divided PDs to estimate pixel value of the other of the divided PDs by performing a calculation.
When the divided PDs disclosed in Japanese Patent Laid-open No. 2001-83407 and Japanese Patent No. 4691930 are saturated, excess charges due to the saturation (charges corresponding to the saturation) leaked to adjacent divided PDs. Therefore, deterioration is caused in a phase difference image by a signal of a divided PD corresponding to the same micro lens with a saturated divided PD due to the leakage of the excess charges. In view of this, it is preferred that saturation detection is performed in each divided PD before focus detection to perform a focus detection process by taking saturation of each divided PD into consideration.
However, when a signal of each of the divided PDs is converted into a luminance component signal before the saturation is detected in the configuration disclosed in Japanese Patent No. 4691930, the other luminance component signal is to be calculated based on the calculation of the luminance component signals, and thus, an original signal of each of the divided PDs corresponding to the calculated luminance component signal cannot be recognized. As a result, it is difficult to perform highly accurate focus detection.